HIGH-PRESSURE CLEANER WITH AN AUTOMATIC CONTROL UNIT

Abstract: In a high-pressure cleaner having an automatic control unit (12) comprising a piston rod (20) with a piston (21), a first side (22) of which is subjected to the pressure in the suction inlet of an injector carrying the liquid flow to the cleaning gun and the other side (23) of which is subjected to the output pressure of the pump connected to the drive nozzle of the injector, so as to move the piston (21) in dependence on said pressures so as to either close a switch (16) in the supply circuit of the pump motor or to open a pressure-release valve (27, 33) connecting the space bounded by the second side of the piston (21) with a pressure-release chamber (26) connected to the inlet of the pump, the novel feature is that the effective areas on the two sides of the piston (21) are different and attuned with the characteristics of springs (28, 29) acting upon the piston (21) in a contact-closing direction in such a manner, that when the flow of liquid is shut off by closing the valve in the cleaning gun, the piston (21) and hence the piston rod (20) will take up an intermediate, equilibrium position, in which the pressure-release valve (27, 33) is closed and the switch (16) is not held in the contact-connecting position.

Description: HIGH-PRESSURE CLEANER WITH AN AUTOMATIC CONTROL UNIT TECHNICAL FIELD The present invention relates to a high-pressure cleaner of the kind comprising a) an inlet for liquid at a relatively low pressure, b) a high-pressure pump, the suction side of which is connected to the liquid inlet and the pressure side of which is connected to c) the drive-nozzle inlet in an injector, the outlet of which is connected to a cleaning gun, and d) an automatic control unit comprising dl) a cylinder chamber in which a spring-loaded piston is sealingly and slidingly supported and hence divides the cylinder chamber into two part- chambers of which the first is connected to the suction inlet of the injector and the second is connected to the pressure side (8) of the pump, d2) a pressure-release chamber separated from the second chamber by a partition with a through-going opening, and d3) a piston rod secured to the piston and from the latter extending partly through the first chamber and sealingly and slidingly through an opening in the external wall of the first chamber for engagement with the operating member of a switch inserted in the power supply circuit of the drive motor for the pump, partly through the second chamber and slidingly through the opening in the partition, with which opening it co-operates to form a pressure-release valve, said valve being closed when the piston rod is in a first position (Figure 2) , in which the first chamber is relatively small and the piston rod keeps the switch in a contact-connecting posi- tion, and open when the piston rod is in a second position (Figure 3) , in which the first chamber is larger than in said first position and the piston rod does not keep the switch in the contact-connect- ing position. BACKGROUND ART When operating high-pressure cleaners of the kind de¬ scribed above, situations may arise, in which a relatively high pressure of e.g. 80-100 bars prevails on the pressure side of the pump without there being any possibility of relieving this pressure. DISCLOSURE OF THE INVENTION It is the object of the present invention to provide a high-pressure cleaner of the kind described above, that does not suffer from the disadvantage described above, and this object is achieved with such a high-pressure cleaner, according to the invention being characterized in e) that the effective surface areas on both sides of the piston, being greater on the side facing the first cham¬ ber than on the opposite side, and the characteristics for the spring or springs, with which the piston is bi- ased, are mutually attuned in such a manner, that when substantially equal moderate pressures reign in the two chambers, the piston and with it the piston rod will take up an equilibrium position or third position (Fig¬ ure 4) situated between said first and second positions and in which the pressure-release valve is closed and the piston rod does not keep the switch in the contact- connecting position. With this arrangement, closing of the valve in the clean- ing gun after a period of normal operation will cause the piston and hence the piston rod to take up said second position, in which the pressure-release valve is open, thus releasing some of the pressurized liquid towards the inlet side, to which the pressure-release chamber is connected, after which the piston and hence the piston rod will make a partial return to the equilibrium position or third position referred to in item e bove, in which the pressure in the space comprising pressure side of the pump is held at an intermedia" alue, i.e. 20 bars, sufficiently low to avoid any riss::. and sufficiently high to provide operating pressure for the switch to supply power to the pump motor, when the valve in the cleaning gun is re-opened. According to a first preferred embodiment, the spring- biasing of the piston is provided by at least two heli¬ cal compression springs placed in the second chamber, of which at least one spring acts upon the piston solely along a part of the total path of movement of the piston. According to a second preferred embodiment, the pressure- release valve is constituted by a) the opening extending through the partition and having a cylindrical surface, and b) a cylindrical valve member secured to or integral with the piston rod and co-operating slidingly and seal¬ ingly with the cylindrical surface in the opening, said valve member comprising a pressure-re e channel adapted to connect the second chair.-er with t .ressure-release chamber solely in said second position ■.Figure 3) . According to a third preferred embodiment, the sealing function between the cylindrical wall in the opening and said valve member is effected by an O-ring situated in a circumferential groove in the cylindrical surface. BRIEF DESCRIPTION OF THE DRAWINGS In the following detailed portion of the present descrip¬ tion, the invention will be explained in more detail with reference to the exemplary embodiment of a high- pressure cleaner according to the invention shown in the drawings, in which Figure l is an overall view showing diagrammatically the parts of a high-pressure cleaner relevant to the present invention including the automatic control unit, and Figures 2-4 at a larger scale show the automatic control unit of Figure 1 in three different states of operation. DESCRIPTION OF THE PREFERRED EMBODIMENT The high-pressure cleaner shown diagramatically in Figure 1 comprises a supply conduit 1 adapted to be connected to a suit- able source of cleaning liquid, normally water, such as a water-mains connection, a high-pressure pump assembly 2 comprising - an inlet valve 3, - a cylinder 4 with a reciprocating piston 5, - a drive motor 6, and - an outlet valve 7 leading to a first high-pressure conduit 8 leading to - the drive-nozzle inlet in an injector 9, the outlet of which is connected to - a second high-pressure conduit 10 leading to - a cleaning gun 11 adapted to eject a jet of clean¬ ing liquid at a high velocity. With the exception of the injector 9, the parts 1-11 men- tioned above function in a manner known in principle in causing a jet of liquid to be ejected from the cleaning gun 11, this gun for control purposes having a manually operable valve (not shown) capable of interrupting the connection between the second high-pressure conduit 10 and the gun's nozzle. The high-pressure cleaner diagrammatically shown in Figure 1 also comprises an automatic control unit 12, connected hydraulically through a first pressure-release conduit 13 to the supply conduit 1, through a second pressure-release conduit 14 to the first high-pressure conduit 8, and - through a control-pressure conduit 15 to the suction inlet of the injector 9. Electrically, the automatic control unit 12 is connected through an ON/OFF switch 16 connected in a manner not shown to the supply circuit of the drive motor 6. The automatic control unit 12 and the manner in which it co-operates with the remainder of the high-pressure clean¬ er will now be described with reference to Figures 2-4 in conjunction with Figure 1. The automatic control unit 12 shown in Figures 1-4 com¬ prises a substantially cylindrical housing 17 that is hollow and permanently closed at one of its ends, while the opposite end is closed by a gland 18 co-operating with a stationary transverse wall 19 to act as a guide for a piston rod 20, to which a piston 21 is secured. The piston 21 divides the space between the gland 18 and the transverse wall 19 to form two chambers, i.e. a first chamber 22 between the gland 18 and the piston 21 and a second chamber 23 between the piston 21 and the transverse wall 19. At its end shown to the right in Figures 1-4, the piston rod 21 comprises an extension 24, the free end of which is capable of abutting against the operating member 25 of the ON/OFF switch 16 already referred to above. The contacts of the switch 16 are so arranged, that electrical power may be supplied to the drive motor 6 in the pump assembly 2 when the operating member 25 is depressed as indicated in Figure 2. The space within the housing 17 to the left of the trans¬ verse wall 19 constitutes a pressure-release chamber 26 adapted to communicate with the second chamber 23 when the piston rod 21 is in the position shown in Figure 3, in which a pressure-release channel 27 formed in the piston rod 21 connects the two chambers with each other. The second chamber 23 accommodates two helical compression springs, i.e. a first spring 28 constantly urging the piston 21 towards the gland 18, and a second spring 29 also urging the piston 21 towards the gland 18, but not further than to the position shown in Figure 3, so that only the first spring 28 acts on the piston 21 in the position shown in Figures 2 and 4. A stop abutment 30 limits the extent of movement of the piston 21 towards the right in the drawing, and the ex¬ tension 24 of the piston rod 20 extending through the gland 18 is preferably so dimensioned that under no cir¬ cumstances will the operating member 25 be depressed beyond its normal contact-connecting position. As will be evident from Figure 1, the first chamber 22 is connected to the suction inlet in the injector 9 through the control-pressure conduit 15, the second chamber 23 is connected to the first high-pressure conduit, i.e. the pressure side of the pump, through the second pressure- release conduit 14, while the pressure-release chamber 26 is connected to the supply conduit 1 through the first pressure-release conduit 13. It will be seen that the effective area of the side of the piston 21 facing the first chamber 22 is bigger than the effective area of the side facing the second chamber 23. This means, of course, that with equal pressures on both sides of the piston 21, there will be a net force urging the piston towards the left, i.e. from the position shown in Figure 2 towards the position shown in Figure 3. It will also be appreciated that, due to the arrangement of the two springs 28 and 29, the relationship between the position of the piston 21 and the spring force acting upon it will not be a simple linear one, but rather a composite linear relationship, the steepest part of which corresponds to the region in which both springs are ac- tive. This again means that the piston 21 may find an equilibrium position, in which the forces due to the action of the springs 28 and 29 are counterbalanced by the net pressure force. In the operating position shown in Figures 1 and 2, the pump pressure P2 is higher than the control pressure P3 in the control-pressure conduit between the suction inlet of the injector 9 and the first chamber 22 in the control unit 12. Although the area of the piston 21 acted upon by the pump pressure P2 is less than the area acted upon by the control pressure P3, the control pressure P3 is - due to the intense flow of liquid from the pump assembly 2 to the cleaning gun 11 through the injector 9 - so low that the piston 21 is urged towards the gland 18 against the stop abutment 30, thus holding the switch 16 in the contact-connecting position enabling electrical power to be supplied to the drive motor 6. When the valve (not shown) in the cleaning gun 11 is closed, the pressure P3 will immediately rise so as to become equal to the pump pressure P2, so that equal pressures reign on both sides of the piston 21, producing a net force urging the piston away from the gland 18 to the position shown in Figure 3. This causes the switch 16 to interrupt the current to the motor 6, which then stops. The pressure P2 and - due to the connection through the injector 9 - also the pres¬ sure P3 will be released through the pressure-release channel 27 to the pressure-release chamber 26, in which inlet pressure reigns. When the pressure has decreased to approximately 20 bars, the net hydraulic force on the piston 21 is reduced sufficiently for the first spring 28 to move the piston 21 back into the intermediate posi¬ tion shown in Figure 4, this being an equilibrium posi¬ tion. The pressure and the space comprising the conduits 14 and 15 and the chambers 22 and 23 will now remain constant, as the pressure-release channel 27 has moved to a position, in which it no longer connects the second chamber 23 to the pressure-release chamber 26. In this position, the switch 16 is still in the OFF position. Upon re-opening of the valve in the cleaning gun 11, the pressure of approximately 20 bars in the above-mentioned space comprising the conduits 14 and 15 and the chambers 22 and 23 will decrease to atmospheric pressure due to this space now being connected to atmosphere through the gun 11, causing the net hydraulic force on the piston 21 to be reduced further so as to allow the first spring 28 to move the piston 21 back to the position shown in Fig- ures 1 and 2, thus re-establishing normal operation. As the switch 16 is only closed when there is a sufficient flow of liquid through the injector 9 , an auxiliary start¬ ing contact (not shown) may be necessary to supply elec- trical energy to the drive motor 6 until such flow has been established. Such a contact could be a "short-make" contact operated by the trigger in the cleaning gun 11. As will be seen from especially Figures 2-4, the various points in need of a seal are provided with O-rings or the like not referred to specifically, as persons skilled in this art will know how to devise and place such seals. One feature is, however, worthy of mentioning: The placing of the O-ring 31 in a circumferential groove 32 in the inner cylindrical surface 33 in the transverse wall extending about the part of the piston rod 20 in which the pressure- release channel 27 is formed. When looking at Figures 2- 4 and considering that the pressure in the second chamber 23 is always higher than the pressure in the pressure- release chamber 26, it will be seen that under no circumstances will the O-ring 31 be urged against the orifice of the pressure-release channel 27 facing it. With an opposite arrangement, i.e. with the pressure- release channel 27 formed in a stationary element surrounding a movable valving element on the piston rod 20 comprising an O-ring in an outwardly open groove, there would be a risk of the O-ring being urged towards the orifice of the pressure-release channel and gradually being worn down by the shearing action of the edges of the orifice. List of parts 1 supply conduit 2 pump assembly 3 inlet valve 4 cylinder 5 piston 6 motor 7 outlet valve 8 first high-pressure conduit 9 injector 10 second high-pressure conduit 11 cleaning gun 12 automatic control unit 13 first pressure-release conduit 14 second pressure-release conduit 15 control-pressure conduit 16 ON/OFF switch 17 housing 18 gland 19 transverse wall 20 piston rod 21 piston 22 first chamber 23 second chamber 24 extension 25 operating member 26 pressure-release chamber 27 pressure-release channel 28 first spring 29 second spring 30 stop abutment 31 O-ring 32 circumferential groove 33 cylindrical surface

Claims: C L A I M S 1. High-pressure cleaner of the kind comprising a) an inlet (1) for liquid at a relatively low pres¬ sure, b) a high-pressure pump (2) , the suction side of which is connected to the liquid inlet (1) and the pressure side (8) of which is connected to c) the drive-nozzle inlet in an injector (9) , the outlet of which is connected to a cleaning gun (11) , and d) an automatic control unit (12) comprising dl) a cylinder chamber (22, 23) in which a spring- loaded (28, 29) piston (21) is sealingly and slidingly supported and hence divides the cylinder chamber into two part-chambers (22, 23) of which the first (22) is connected to the suction inlet of the injector (9) and the second (23) is connected to the pressure side (8) of the pump (2) , d2) a pressure-release chamber (26) separated from the second chamber (23) by a partition (19) with a through-going opening (33), and d3) a piston rod (20) secured to the piston (21) and from the latter extending partly through the first chamber (22) and sealingly and slidingly (24) through an opening in the external wall (18) of the first chamber (22) for engagement with the operating member (25) of a switch (16) inserted in the power supply circuit of the drive motor (6) for the pump, partly through the second chamber (23) and slidingly through the opening (33) in the partition (19) , with which opening it co-operates to form a pressure-release valve (33, 27), said valve being closed when the piston rod (20) is in a first position (Figure 2) , in which the first chamber (22) is relatively small and the piston rod (20) keeps the switch (16) in a contact-connecting position, and open when the piston rod (20) is in a second position (Figure 3) , in which the first chamber (22) is larger than in said first position and the piston rod (20) does not keep the switch (16) in the contact-connecting posi¬ tion, characterized in e) that the effective surface areas on both sides of the piston (21) , being greater on the side facing the first chamber (22) than on the opposite side, and the characteristics for the spring or springs (28, 29), with which the piston (21) is biased, are mutually attuned in such a manner, that when substan- tiall equal moderate pressures reign in the two chambers (22, 23), the piston (21) and with it the piston rod (20) will take up an equilibrium position or third position (Figure 4) situated between said first and second positions and in which the pressure- release valve (33, 27) is closed and the piston rod (20) does not keep the switch (16) in the contact- connecting position. 2. High-pressure cleaner according to claim 1, charac¬ terized in that the spring-biasing of the piston (21) is provided by at least two helical compression springs (28, 29) placed in the second chamber (23), of which at least one spring (29) acts upon the piston solely along a part of the total path of movement of the piston. 3. High-pressure cleaner according to claim 1 or 2, characterized in that the pressure-release valve (33, 27) is constituted by a) the opening (33) extending through the partition (19) and having a cylindrical surface, and b) a cylindrical valve member secured to or integral with the piston rod (20) and co-operating slidingly and sealingly with the cylindrical surface in the opening (33) , said valve member comprising a pressure-release channel (27) adapted to connect the second chamber (23) with the pressure-release chamber (26) solely in said second position (Figure 3). 4. High-pressure cleaner according to claim 3, characterized in that the sealing function between the cylindrical wall in the opening (33) and said valve member is effected by an O-ring (31) situated in a circumferential groove (32) in the cylindrical surface.

Inventors: STRANDGAARD JAN, STRANDGAARD, JAN
Applicants: KEW IND AS, STRANDGAARD JAN, KEW INDUSTRI A/S, STRANDGAARD, JAN
Application year: 1994
Main classification: B08B3
IPC codes: B08B3